In recent years, in a manufacturing process of a semiconductor device, a method called chemical oxide removal (COR) which chemically performs etching within a chamber without generating plasma draws attention as a miniaturization etching technique substituted for plasma etching.
As the COR, there is known a process in which a silicon oxide film (SiO2 film) existing on a surface of a semiconductor wafer as a target object is etched within a chamber held in a vacuum by causing a hydrogen fluoride (HF) gas and an ammonia (NH3) gas to be adsorbed onto and react with the silicon oxide film to generate ammonium fluorosilicate ((NH4)2SiF6; AFS), and sublimating the ammonium fluorosilicate by heating the same in a subsequent step.
In recent years, a film (an ALD-SiO2 film) formed by an atomic layer deposition method (an ALD method) is often used as a SiO2 film which is formed in a manufacturing process of a semiconductor device. Another SiO2 film (a thermal oxide film, etc.) formed by methods other than the ALD method, is sometimes formed adjacent to the ALD-SiO2 film. As such, it is required to etch the ALD-SiO2 film with high selectivity with respect to the thermal oxide film or the like. However, the use of the HF gas and the NH3 gas makes it difficult to etch the ALD-SiO2 film with a sufficiently high selectivity with respect to another SiO2 film such as the thermal oxide film or the like.